It is manifest that the accidents which are _separable_ from the individual substance, _e.g._ name, shape, size, appearance, location, etc., cannot constitute its individuality. There are, however, other characteristics which are _inseparable_ from the individual substance, or which are _properties_ of the latter, _e.g._ the fact that an individual man was born of certain parents. Perhaps it is such characteristics that give its individuality to the individual substance?(144) To think so would be to misunderstand the question under discussion. We are not now inquiring into the _extrinsic_ causes whereby actually existing reality is individuated, into the _efficient_ principles of its individuation, but into the _formal_ and _intrinsic_ principle of the latter. There must obviously be something intrinsic to the individual reality itself whereby it is individuated. And it is about this intrinsic something we are inquiring. The individual man is this individual, human nature is thus individuated in him, by something that is essential to human nature as found in him. This something has been called—after the analogy of the _differentia specifica_ which differentiates species within a genus—the _differentia individua_ of the individual. It has also been called by some the _differentia numerica_, and by Scotists the _haecceitas_. However we are to conceive this something, it is certain at all events that, considered as it is really found in the individual, it cannot be anything _really distinct_ from the specific nature of the latter. No doubt, the _differentia specifica_, considered in the abstract, it is not essential and intrinsic to the _natura generica_ considered in the abstract: it is extrinsic and accidental to the abstract content of the latter notion; but this is because we are conceiving these grades of being in the abstract. The same is true of the _differentia individua_ as compared with the _natura specifica_ in the abstract. But we are now considering these grades of reality as they are actually in the concrete individual being: and as they are found here, we have seen that a real distinction between them is inadmissible.